Pusher mechanisms for fork-lift trucks and the like have been utilized for many years and the use of chain structures for actuating such a pusher mechanism likewise have been known.
Prior Nagin Pat. No. 3,021,024, issued on Feb. 13, 1962 illustrates a chain actuated pusher structure.
Pusher structures of this type, including that of such prior patent, have all employed a generally common type of overall structure, in which a base structure is carried by the lift truck carries the power source for actuating the pusher structure as well as the drive means therefor, with the actual pusher structure being relatively lightly constructed, consistent with its pushing function, and primarily comprising a unitary structure which is movable toward and away from the base structure. Thus, in the prior patent above referred to, the base structure carried the actuating means, i.e. sprockets for the respective chain elements, the power source for driving such elements, the storage means for the adjacent ends of the chains when the pusher structure is in a retracted position etc., whereby all of the actuating structure with the exception of the connecting portions of the chains between the base structure and the pusher structure were disposed on and carried by the base structure. The pusher structure in such case merely provided an adequate pushing base adapted to engage the object being moved, with the only other items being the connection means for the adjacent free ends of the actuating chains.
More recently the use of pusher structure in connection with loads supported on sheet material, rather than pallets and the like, have been more extensively utilized. In this case the load, which may comprise several objects, is supported on a sheet of heavy board stock or other material capable of supporting the load with the pusher structure being provided with a gripper structure whereby the edge of the load-supporting sheet may be firmly gripped, and, by means of retracting movement of the pusher structure, drawn upon the platen or tines of the pusher device. When such a load is to be removed from the pusher device it is merely pushed off of the same by means of the pusher structure, the gripper, in such case, not actually being required.
It will be apparent that with such "slip-sheeted" loads the pusher device must be provided with a suitable gripper structure to enable the sheet carrying the load to be gripped and then moved onto the platen structure of the mechanism. Consequently, the pusher structure must be provided with such a gripper structure as well as the actuating means therefor, for example a hydraulic cylinder. As a result of the required construction, pusher devices including sheet-grippers have involved a relatively thick or heavy base structure, adequate to contain all the actuating mechanism for the pusher structure, while the latter likewise has been of relatively heavy construction, as it now is required to also carry the gripper mechanism including the actuating cylinder or other actuating means therefor. Consequently, such base and pusher structures required and occupied a relatively large minimum amount of space in fore and aft direction, i.e. when the pusher member was in its fully retracted position, which in many cases was 7 inches or more. It will be appreciated that as all of this structure is carried by the lift truck ahead of the front wheels thereof and with the load to be supported thereby disposed ahead of the pusher mechanism, any increase or undesired thickness in such direction of the pusher device as well as increase or excessive weight in the pusher structure results in a corresponding reduction in the total load capacity of the lift truck, as the entire load must be countered by the weight of the truck, and in particular with respect to its center of gravity relative to the front axle thereof, i.e. at the opposite side thereof to the load being carried thereby.